autcross: simplify code using complement() and intersecting_word()

* bin/autcross.cc: Let complement() decide how to complement automata.
Do not apply remove_fin(), because we have a generic emptiness check
now.  Use intersecting_word() instead of product()+accepting_word() so
that the former can maybe be optimized in the future.
* tests/core/autcross2.test: Adjust test case to use TGBA instead
of monitors, as calling complement() had a side-effect of setting
the "weak" property on the input.
13 jobs for next in 121 minutes and 21 seconds (queued for 1 second)
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